Spectroscopic and photochemical studies of several electron transfer proteins are proposed. The principal objectives are to (1) examine the catalytic mechanisms employed in oxygen reduction and related reactions by copper enzymes, (2) study electronic interactions among the copper sites in these enzymes, (3) spectroscopically characterize a new series of nickel(II) derivatives of blue copper proteins, and (4) elucidate the distances involved in electron transfer from the copper sites in proteins to electronically excited metal complexes in aqueous solutions.